Evaluating the Techno-Economic Feasibility of Forward Osmosis Process Utilizing Low Grade Heat: Applications in Power Plant Water, Wastewater, and Reclaimed Water Treatment
Recovering and using uncoverted heat produced during electric power generation holds potential to significantly improve the efficiency of the electric power industry. One potential use of this low-temperature waste heat is on-site water treatment using waste heat driven processes to comply with the 2015 Effluent Limitation Guidelines for the Steam Electric Generating Sector. Ammonia-carbon dioxide forward osmosis (NH 4 HCO 3 FO) is a two-step waste heat driven process that involves a membrane separation process in which an osmotic pressure gradient created by an NH 4 HCO 3 draw solution is used to pull water across the membrane and a distillation column to regenerate the NH 4 HCO 3 draw solution. In this work we estimate the quantity, quality, and spatio-temporal availability of waste heat produced at U.S. coal, nuclear, and natural gas plants. We combine these estimates of waste heat availability with a techno-economic optimization model of NH 4 HCO 3 FO in order to assess the potential of NH 4 HCO 3 FO to treat flue gas desulfurization (FGD) wastewater, gasification wastewater, and boiler feedwater. We find that in 2012, 18.9 billion GJ of waste heat was discharged from the U.S. coal, natural gas, and nuclear fleet, although only 900 million GJ of waste heat was discharged at temperatures suitable for NH 4 HCO 3 FO. A maximum of 1.9 billion m3/yr of water could be produced using this waste heat to drive a NH 4 HCO 3 FO. The costs of waste heat driven NH 4 HCO 3 FO for FGD and gasification wastewater treatment to zero liquid discharge (ZLD) and boiler feedwater treatment are 2.20-2.40/m 3 and 0.35-0.65/m 3 , respectively. With mechanical vapor compression and crystallization for ZLD wastewater treatment and reverse osmosis for boiler feedwater treatment as the cost benchmark technologies, waste heat driven NH 4 HCO 3 FO is cost competitive for ZLD wastewater treatment, but not boiler feedwater treatment.